Vacuum tube



Jan. 18,1938. H. G. CORDES VACUUM TUBE Filed Oct. 24, 1927 5Sheets-Sheet 1 F E L;

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H. G. CORDES Jan. 18, 1938.

VACUUM-TUBE Filed Oct. 24, 1927 5 Sheets-Sheet 4 IN V EN TOR Hz/7r 6.Cordas wgdfigw A TTO NE YS H. G. CORDES Jan. 18, 1938.

VACUUM TUBE 5 Sheets-Sheet 5 Filed 001;. 24, 1927 s s a v. d r R 0 TWORC T m M m6 v9 Mr M r H Y B with a mercury Patented Jan. 18, 1938 VACUUMTUBE Henry G. Cordes, Palo Alto, can; Bertha L.

Cordes, owner by decree of court Application October 24, 1927, SerialNo. 228,233 30 Claims. (01.175-354) This invention relates generally todevices utilizing electrical discharges .thru gases, and is particularlyapplicable to mercury vapor vacuum tubes. The devices herein describedare capable of being used for the rectification of high voltagealternating'current or for the production of high frequencyuni-directional current discharges from a source of continuousuni-direccan be rectified by intermittent discharges thru tionalcurrent.

It is an objectof this invention to devise means for more eifectivelycontrolling current discharges thru gases, particularly currentdischarges thru ionized mercury vapor.

It is a further object of this invention to devise a mercury arcrectifier capable of rectifying higher voltages than has heretofore beenpos- 81 e.

It is a further object of this invention to devise a mercury vapor tubecapable of interrupting flow of relatively large currents of high Ptential.

It is a further object of this invention to devise improved meanswhereby relatively small currents may be utilized for -piloting orcontrolling relatively large current discharges.

It is a further object of this invention to devise a'mercury arc vacuumtube which will not permit aninverse flow of current when used togetherwith reactive circuits.

Further objects of the invention appear from the following descriptionin which I have set forth the preferred embodiments of my invention; Itis to be understoodthat the appended claims are to be accordeda range ofequivalents consistent with the state of the prior art.

Referring to the drawings:

Figure 1 is a side elevational view in cross section illustrating amercury vapor vacuum tube incorporating theprinciples of this invention.

Fig. 2 is a view similar to Fig. 1 but showing a modified form 'of theanode chamber and its associated electrodes.-

Fig. 3 is a view similar to Fig. 1 showing a further modification of theinvention, and also showing the manner in which the device may beutilized for the generation of high frequency oscillations.

.Fig. 4 is a view similar to Fig. 1 showing a further modification ofthe invention, this modification differing in construction of themercury pump and the details of the control electrodes.

Fig. 5 is a cross sectional detail illustrating another modified form ofanode chamber and its associated electrodes, capable of being utilized hvapor tube such as shown in Figs. 6 and '7 are details in cross sectionshowing modified forms of ionizing anodes.

Fig. 8 is a detail shownin cross section of another modified form ofanode chamber and associated electrodes, capable of being utilized witha vacuum tube such as shown in Fig. 1.

Fig. 9 is a cross sectional elevational view showing a further modifiedform of tube.

Fig. 10 is a crosssectional detail taken along the line l0l0 of Fig. 9.

The value of alternating current voltage which mercury vapor in a vacuumtube is limited by ,arc-back when the inverse voltage exceeds a cer tainmaximum value or by excessive inverse 'Geissler discharge currentwhen-the discharge frequency is high. For this reason it has been.

. impossible in the past to utilize mercury vapor -reduce high frequencyinverse current to a negligible value when producing high frequencyunidirectional discharges.

It is well known that a low pressure of gas, either in the form ofnon-condensable (fixed gas) or condensable gas (vapor), is essential ina mercury vapor tube when it is desired to avoid ex-, cessive inversecurrent. Consequently, in mercury vapor tubes for rectifying highvoltages, it has been the practice to keep the gas pressure as low aspossible. However, when the gas pressure is decreased below a certainpoint a phenomenon known as fading occurs in rectifiers. Fading consistsin an anode failing to pass current during part or all of a positivehalf-cycle due to the establishment of a high initial resistance in thedischarge path space, that is, the space acts as an insulator untilbreakdown is produced by a relatively high positive potential impressedon the anode. In addition to low gas pressure, fading is known to beincreased by lengthening the discharge path, by reducing itscross-sectional area, or by placing bends in it. The cause of fading isgenerally attributed to the formation of a static charge on the glasswall of a low pressure part of the discharge path.

. has been known as a means for neutralizing the static charge. Myinvention comprises means for reducing the gas pressure to a lower valuethan has heretofore been used and providing more eflective means'toneutralize the static charge.

The effects of charging conductors which are insulated from, and placedadjacent to, the discharge path has been published. The phenomena causedby the effects consists in either decreasing or increasing the breakdownvalueof the discharge path space. In terms of the well known concepts ofcharged elements and of space charge of the electron theory, thebreakdown value is decreased by increasing the number of positive ionsin the discharge path space and it is increased by decreasing-the numberof positive ions. In other words, the breakdown value varies with thenegativity of the space charge. I have found that the breakdown valuecan be thus varied more effectively as the rarefaction of the space isincreased, Fading is attributed to the collection of positive ions fromthe space by the wall of the discharge path, especially when therarefaction is high. I reduce undesired negativity by making the spacemore positive.

The starting band, or the filamentary exten-- sion of the anode, in amercury vapor lamp to start the discharge constitutes a well known meansfor decreasing the breakdown value of the path space. On the other hand,metallic rectifier tubes are often constructed so that the anode issurrounded by the metal of the tube which is at the potential of thecathode and therefore tends to attract positive ions from the spacearound the anode; this tends to increase the breakdown value of thedischarge path space. It is customary practice to place a shield aroundthe anode to reduce the tendency of the metal to make the space chargetoo negative.

One feature of my improvement consists in establishing a desiredbreakdown value of the discharge path space and then cyclically varyingthis value to attain the result desired.

The breakdown-value-control surface may be either a metallic conductorplaced in the discharge path space or a conducting sheath placedadjacent to the glass opposite to the space. In

the first case the discharge current may concentrate at one point on themetallic conductor which may thereby become a source of secondaryelectron emission. In the second case a charge is distributed over theentire glass surface thus avoiding concentration and secondary electronemission. The sheath acts in a manner equivalent to a number ofcondensers (capacitive impedances) each in series with a metalliccontrol conductor. Undesirable concentration of the discharge currentmay also be avoided by uti lizing a high resistance conductor in amanner hereinafter described. The terms control surface and controlconductor, as here used, control space charge including wall chargeeffects as distinguished from control of the state of ion emission fromthe cathode whether produced] by heating the mercury, by passing akeep-alive current to the cathode, or by passing a. pilot spark to thecathode,

To prepare a tube in the practice of this invention, I initially outgasthe tube and electrodes r to a very high degree and provide means, aftersealing oil, to maintain the required low gas pressure in the anode endof the discharge path which will hereinafter be termed the anode chamberby restricting the flow of mercury vapor into the anode chamber, byproviding a cooling medium such as water or other refrigerant to coolthe anode chamber, by providing diffusion and condensation pump action,and by providing Sprengel pump action.

The restriction of mercury vapor flow has been side of the constrictedpart of the discharge path. The high pressure side when viewed thruwater and pyrex glass has a yellowish-white glow while the low pressureside has a' bluish glow which indicates much greater diffusion of thedischarge.

I- have found that a great tendency for high frequency intermittentdischarges to take place is produced by an abrupt change in thecrosssectional area.of the discharge path at the low temperatureproduced by a, cooling medium.

The practice of producing diffusion and condensation pump action in amercury vapor tube is old. The novel feature of my invention comprises ahigher vapor pressure in the cathode chamber than has heretofore beenused to supply pumping vapor. I provide an external heater to heat thrua glass heat-conductor the cathode mercury both to produce a preliminarypumping action and to reduce the breakdown value of the discharge pathspace by increasing the vapor pressure in the cathode chamber. Theheater also reduces the breakdown value when the rectified current istoo small to maintain the cathode mercury at the proper temperature.

Another novel feature is a miniature Sprengel pump which removespermanently non-condensable gas from the operating part of the tube. Thereturn-flow of condensed mercury passes thru a miniature fall tube andnon-condensable gas is thereby compressed and liberated in a separatechamber which is sealed by mercury from the main part of the tube. Anymercury vapor tube may be made self-evacuating during operation byproviding the tube with such a pump.

Referring now to that embodiment of the invention illustrated in Fig. l,I have shown a vacuum tube II which is made of pyrex and which isevacuated to a high degree. The upper part of the tube is formed toprovide an anode chamber I2 while the lower part is formed to provide acathode chamber l3. Cooperatively associated with the anode chamber isan anode I4 to which is connected the lead-in terminal Hi. The anode iscylindrical in form and is made of pressed graphite, altho it may bemade of metal and may assume another form. The cathode chamber is formedto provide a receptacle for the cathode mercury H to which connection ismade by the lead-in terminal N! which is grounded.

The anode chamber is cooled by means of a jacket l9 thru which coldwater is circulated. The cathode chamber is heated by an electricalheater 2| supplied with current thru terminals 22 and 23. A heatinsulating medium 24 is employed for minimizing transfer of heat fromthe cathode chamber or from the heater to the anode chamber. In additionto the usual anode and cathode, I provide a breakdown control surface bymeans of which I control discharges thru the anode chamber. In Fig. 1the control surface is formed by the inner surface of the water-cooledglass which is charged by displacement current flowing to or from theconducting water in the cooling jacket l9.

Instead of having an unrestricted path for mercury vapor between theanode and cathode chambers, the mercury vapor from the cathode chamheris discharged into the lower part of the anode chamber thru a suitabletube 21, the discharge end of which is substantially smaller in diameterthan that of the anode chamber l2. Positioned over the end of tube 21 isa vapor-deflecting cap 28 which is suitably supported (not shown) sothat its periphery is spaced as shown from the anode chamber wall. Thiscap or deflector serves as a means for restricting flow of mercury vaporfrom the cathode to the anode chamber, directs vapor flow away fromanode l4, and separates the anode. chamber which lies above the rim ofthe cap'from the condensing chamber which is disposed below said rim.The deflected mercury vapor is condensed as it contacts with the cooledwall below the cap. The condensed mercuryis returned to the cathodechamber by way of one or more fall tubes 29 which discharge into asuitable trap 30; the mercury from this trap being returned to thecathode chamber thru tube 3|.

Fall tube 29 is of relatively small diameter so that Sprengel pumpaction is produced by condensed mercury dropping down thru the 'same.This Sprengel pump action assists the condensation pump action inreducing the pressure in the anode chamber and transfers permanentlynon-condensable gas from the main part of the tube to the gas-chamber35. I have found that the mercury in trap 30 in the lower end of falltube 29 which seals the gas in chamber 35 from the main part of theevacuated space of the tube is outgassed to a greater degree than themercury ll of the cathode to which it is returned. The resistance 15represents the resistance of the water (not shown) from the ground.

' In order to explain the operation of the device. it will be assumedthat terminals l6 and I8 are connected to a suitable source ofcurrentwhile by means of a double throw switch 32 terminal 26 may be connectedeither to terminal 16 orto terminal 33'upon which controlling potentialsare applied. The cathode chamber is heated by supplying alternatingcurrent to the terminals 22 and 23 until the mercury vapor pressure inthe cathode chamber attains a value of the order shown in the drawingswhich corresponds to a breakdown value of potential of the order of 1500volts. Assuming now that switch .32 is open, that an alternatingpotential of about 15,000 volts is applied to terminals l6 and i8, thatpumping action is'taking place due to the mercury vapor flowing downpast the rim of cap 28 and condensing, and that cold water is flowingfrom a grounded source thru supply tubing and jacket iii to cool theanode chamber and charge the water negatively with respect to the anodeM which increases the negativity of the discharge path space, then nobreakdown will take place to initiate a current flow from the anode tothe cathode. Now if conductors l5 and 26 are connected together byswitch 32, flow of current will occur in one direction'only and. thedevice will operate emciently as a rectifier. At a current density ofabout one half ---ampere per square inch, the discharge is bluishbetween anode I 4 and the rim of the'vapor defiector 28 while it isyellowish-white between the deflector and thecathode ii. The usualcathode spot is formed on the cathode provided the external resistancein the supply circuit permits suficient current to flow. If switch 32 isopened again while alternating potential is being applied, the half-wavecurrent discharges between the anode and cathode immediately stop.

In order to illustrate another mode of operation, it will be presumedthat a direct current positive potential is impressed on terminal I6with respect to terminal 18 and switch 32 is thrown to connectconductors 26 and 33. Due to the water being connected to l8 thru highresistance, a discharge'does not take place as long as displacementcurrent fiows from the anode chamber to the water. However, if apositivepotential is Jacket I9 to the.

placed on conductor 33 so that the flow of displacement current ceasesthen breakdown takes place between anode and cathode. I have found thatbecause of the inherent properties of my device unidirectionaldischarges may take place at-relativelyhigh frequencies as controlled bypotentials appliedto conductor '26. The device may therefore beemployedfor the generation of radio frequency oscillating current.

I have found that it is practicable to supply fresh water to jacket l9thru about ten feet of rubber tubing and discharging the water thrusimilar tubing. By operating the tube under such conditions, theexternal resistance (represented by l5) of the two rubber tubes inparallel between the control terminal 26 and the cathode terminal I8 isabout one megohm which allows suiiicient current to pass to operate thetube in the manner described above.

The facts and theory with which I explain the operation of the device isas follows: During a positive half-cycle on the anode, with switch 32open, current cannot be started to flow from anode ll to mercury cathodel1 due to the high negativity of the space charge produced -by the waterin the water-jacket l9 which is electrically connected to the cathodethru the resistance I 5 mentioned above. Closing switch 32 upwardconnects the water in the jacket to the anode 14 which changes thecharge of the water from negativeto zero with respect to the anode; inother words, closing switch 32 neutralizes the high negativity andproduces a lower breakdown value of the discharge path.. During thehalf-cycle that the anode is negative with respect to the cathode andthe water is similarly charged, the increase of breakdown value causedby the presence of the water acts to prevent inverse discharge which, inturn, determines the range of rectification. The water-cooled wallcollects positive ions without producing an objectionable rise intemperature which is prevented by the presence of both the coolingmedium and the distributed collection area; these positive ions would,in the absence of the charged wall, bombard the anode and therebyproduce a condition favorable to inverse current.

The vacuum necessary for the tube will vary depending upon thepotentials with which it is to be operated. During the process ofevacuating my tube I have found that when the fixed gas pressure isstill relatively high, a crest potential of say 14,000 volts will not berectified, as an inverse discharge takes place whether the switch 32 isopen or closed. When the gas pressure as shown by a McLeod gageconnected to the high pressure part of the tube has attained a fairlylow value, say of the order of one bar, then the discharge with switch32 open is erratic and may be accompanied by inverse discharge to acertain extent. Under this condition ofvacuum the inverse dischargeceases when switch 32 is closed to connect conductors I6 and 26. Thetube will 'function'fairly efiiciently under this condition of vacuumaltho slight fluctuations will occur in the rectified current. However,the factor of safety against inverse discharge is small. I prefer tocarry the vacuum to a higher degree which .produces a condition in whichno discharge can the vacuum is preferably carried to a degree at whichno discharge will occur at such potential vious modifications of Fig. 1may be made as,-

for example, passing a. non-conducting cooling liquid thru jacket IS inwhich a metallic film on glass is disposed to serve as a controlconductor to influence breakdown value of the anode chamber.

In Fig. 2, I have illustrated a modified form of Fig. l in which aninternal control electrode is employed to decrease the breakdown valueof the discharge path by neutralizing the efiects on its value producedby the charging of the water in jacket l9, and during the followinghalfcycle to aid by charging the water to produce an increase ofbreakdown value with respect to inverse current. The anode chamber 2l2of the tube 2 is provided with an elongated internal control electrode33; connection is made to 36 by means of lead-in terminal 31. The anode2 is arranged adjacent the upper end of 36, is cylindrical in shape, andsurrounds electrode 36.

228, similar in construction and function to the deflector 28 shown inFig. 1. The electrode 36 is constructed so as to have relatively highresistance between its upper and lower ends, this resistance beinggreater for tubes adapted to be used upon the higher potentials. Inpractice I have obtained good results by making the electrode 36 ofglass covered with a thin film of metal.

suitable resistance material which will retain its resistance when highpotentials are impressed on its terminals and which will not be attackedby mercury vapor. The upper end of tube 221 which discharges vapor fromthe cathode chamber has a restricted discharge orifice 38 which bothincreases the velocity of the vapor and establishes a greater differenceof vapor pressure in the discharge path. I have found that the abruptchange in the cross-sectional area of the discharge path from that inthe anode chamber to that in constriction 38 provides a condition whichfacilitates the production of high frequency discharges.

The anode chamber 2|2 is cooled by means of water-jacket 2l9. By meansof switch 39 the liquid of this jacket may be connected in parallel withcontrol electrode 36. A three-way switch 41 connects the controlelectrode directly to the anode terminal [6, or to this terminal inseries with condenser 42, or, as in Fig. 1, to terminal 33. The mercuryI1 is heated by heater 2| thru the glass wall of the tube which servesas a heat conductor.

The theory with which I explain the operation of the arrangement shownin Fig. 2 is substantially the same as that with respect to Fig. 1. Whenthe potential of the anode H4 and of the control electrode 36 isincreasing positively with respect to the cathode, a discharge takesplace from the lower end of electrode 36 at the breakdown voltage of thehigh pressure vapor which may be in the neighborhood of 2000 volts.After such breakdown each element of area of the electrode 36 primes anadjacent element above it so that the discharge from electrode 36 climbsup until it initiates a main discharge from the anode 2 in a mannersimilar to the well known filamentaryextension-of-the-anode method ofstarting a mercury vapor lamp. In other words the initial discharge fromelectrode 36 neutralizes the neg- Thev lower end of 36 is expanded toform a deflector However I may use instead a rod con- .structed ofcarborundum or silicon or any other ative space charge in a sheathadjacent to its surface and this sheath increases in thickness as thecurrent increases. The high resistance in series with the controlsurface 36, or of the water between conductor 26 and'the glass adjacentto space 212, tends to prevent the flow of a parasitic high frequencycurrent in a circuit comprising .anode 2; the presence of theresistance, I have found, increases the inverse breakdown value of themain discharge path, and tends to prevent puncture of the glass. Ingeneral, the flow of parasitic high frequency current thru the mainanode must be prevented.

In accordance with the above mode of operation, an equivalent of thecontrol eljgptrode 36 may be formed by utilizing a number of separateconductors of progressively increasing length; the shortest cdnductorterminating near the anode 2H and the longest terminating near thedefieetor 228. The shortest of these conductors may be connected to theanode terminal IE or to some external source of controlling potential,and the remainder may be interconnected in series by high resistances orsmall condensers. Each conductor would then initiate a. discharge fromthe conductor immediately above it and therefore progress upwardly andinitiate a discharge from the anode.

The resistance of the electrode 36 will vary with different conditionsof operation. For example its resistance may be about one megohm when10,000 volts effective are being rectified. One factor in the selectionof the proper resistance for electrode 36 is that in order to pilot thedischarge upwardly the resistance per unit length of electrode 36 shouldbe greaterthan the resistance per unit length of sheath space. By sheathspace I refer to the relatively low resistance sheath formed aboutelectrode 36 in which the negative space charge is neutralized and whichinitiates a main discharge. Another factor which requires that theresistance of electrode 36 be high is that a feeble inverse dischargepasses from the cathode to the lower end of 36 at about the same voltageas that which initiates a discharge in the preceding half-cycle. Thisfeeble inverse current increases the negativity of the space charge thusprotecting the anode from a large inverse current discharge.

It will be noted that switch 4| may be thrown so as to connect electrode36 with terminal l6 in series with condenser 42. This arrangement issometimes desirable as it reduces the effective current flowing thruelectrode 36 and also permits a reduction in the resistance of thiselectrode. The electrode 36 may be used to the exclusion of theconnection 26 to the water in jacket 2|9, or it may be used inconjunction with the same by closing switch 39.

A characteristic feature common to all the discharge path breakdowncontrol surfaces is illustrated by the glass surface of the dischargepath opposite the water in jacket M9, by the surface of electrode 36,and by the equivalent electrodes herein described. In each of theillustrations the control surface consists of a plurality of elementalcontrol surfaces arranged so that the elements of surface areinterdependent. For example assume that a decrease of breakdown value isto be produced by electrode 36 to initiate a discharge to anode 2M fromcathode IT. The piloting discharge, that is, the electron flow, passesfirst from the cathode to the nearest-to-cathode end of electrode 36where the vapor pressure is relatively high and spreads to otherelements of surface toward the anode as is the case in starting amercury vapor lamp by means of a filamentary extension of the anode. Theupper elements therefore depend on the lower for a relatively lowbreakdown value and the lower elements depend on the upper to pilot moreeffectively the discharge to the anode. It is thus seen that a dischargecan be initiated at a relatively low potential thru a discharge pathwhich has a relatively high breakdown value due to length, bends, andlow pressure by means of a plurality of elemental control surfacesconnected to the piloting potential source so that the impedance'in thepiloting circuit is decreased as the piloting discharge spreads towardsthe anode.

Fig. 3 shows a further modification of the invention, and illustratesthe manner in which the tube may be used for the generation of highfrequency oscillations. The lower end of the tube in this instance isprovided with a pocket 43 within which is disposed the electricalheating element 44. This construction permits the mercury 3|! tosurround the heater, thus aflording more efllcient transfer of heat. Theexterior of the lower tube portion is preferably provided with a jacket46 of heat insulating material. The water jacket 3 I 9, is preferablyconstructed of some suitable metal such as nickel iron or chrome ironalloy, and is sealed as at 41 to the glass of the cathode chamber, andat 48 to the adjoining walls of the anode chamber. This arrangementmakes possible a lowerpressure in the anode chamber 3l2 than can beobtained by the use of a glass jacket for the reason that the metal moreeffectively conducts the heat to the cooling liquid. Another advantageis that this metal jacket may serve as an electrode and for this purposeI have shown a terminal conductor 49 connected to the walls of the same.

The control electrode 336 in this instance consists of a hollowglasstube having a hollow deflecting cap 328 formed upon its lower end'.Positioned within this tube and within the hollow cap 328, there is aconductor 53, which is connected to an external terminal conductor 31.Arranged adjacent to and preferably surrounding a lateral extension 54of the tube 5| there is the anode 3M to which is connected the terminalconductor l6.

In conjunction with 'the tube 329 for returning condensed mercury to thecathode chamber, I may utilize a cleanup bulb 56 which may contain inauxiliary electrode of tungsten, activated charcoal or other materialfor absorbing gases. After draining thru tube 329 the mercury isreturned to the cathode chamber thru a suitable trap 330. The controlelectrode 336, or anode extension, functions in the same manner asthecontrol electrode shown in Fig. 2. When the anode M4 is chargedpositively with respect to the cathode, no discharge will'take place ifswitch 32 is opened due to the negativity of the space charge, but

when this switch is closed to connect the anode and the controlelectrode, a discharge will take place between the anode and cathode dueto the decrease of negativity of the space charge produced by currentfrom conductor 53 acting thru the glass 328 and 336. The pilotingactionof the control electrode 336 is substantially the same as thatpreviously described with respect to Figs. 1 and 2.

The use of the'metallic water jacket 3l9 makes it possible to use akeep-alive current between this jacket and the cathode. For example Ihave shown a source of direct current potential as represented by thebattery 51, connected across the terminals 48 and I8. With thisarrangement a current is continuously passed from the water Jacket tothe cathode. thus keeping the mercury vapor in the cathode chambercontinuously ion-' ized. The alternating current to be rectified maythen be impressed across terminals I 6 and 49 as anode and water jacket,and the water jacket or terminal 49 may begrounded as indicated byground connection 58. Ifthe tubeshowninr lgdistobeusedexclusively as arectifier of high voltage alternating current, the conductor 53 may beconnected-directly to the anode 3 within the tube.

One circuit with which the device shown in Fig. 3 may be used for thegeneration of high frequency discharges has been shown. In this vindicated by transformer 50, i. e. across the case a suitable source ofdirect current, such as a generator 59, has its positive lead connectedto anode 3 by way of switch 55 and its' negative lead connected to the"keep-alive anode or jacket 3!!! by way of switch 60, a suitable highfrequency choke 6| being inserted in series with the positive lead. Anoscillatory circuit consisting of inductance 62 and capacitance 63 islikewise connected across the anode 3H and jacket 3i9. A suitable masteroscillator 64 is coupled across the keep alive anode or jacket 3l9'andcontrol electrode 336, as by means of stabilizing circuit 66. The outputor work circuit, as indicated at 61, is suitably coupled to theoscillatory circuit as by means'of inductance". The high frequencycontrolling impulses impressed upon. the controlling electrode 336,initiate a series of current discharges from the anode to the cathode ata frequency dependent upon the frequency of the stabilizing circuit 66.

The cathode ionizing current flowing from the water jacket 3!!! to thecathode 3 will reduce the potential required to initiate a dischargebetween the anode and the'water jacket. If this ionizing current issufficiently large the current passed thru the heater 44 may be reducedto zero; in other words the heater may be used only. for startingpurposes. 1

In the modification shown in Fig. 4, no means has been provided forutilizing pump action of the mercury for reducingthe pressure in theanode chamber. The reduction of pressure in the anode chamber in thisinstance is produced solely by cooling the anode chamber and byproviding a greater restriction between the anode and cathode chamber.For example the tube 421 whichv leads mercury vapor from the cathodechamber is provided with a very small discharge orifice 438. Instead ofutilizing the liquid in the cooling jacket 9 for forming a controlelectrode, I provide in this instance an external metal sleeve H whichis connected to the terminal conductor 26. This construction permits theuse of non-conductive cooling liquids, such as cold oils.

In the operation of the modification shown in Fig. 4, the oriflce 438between the cathode and anode chambers permits a very small amount ofmercury vapor to pass from the cathode into the anode chamber and all ofthis mercury is condensed in the lower part of the anode chamof 1 amperethe diameter of this orifice may be.

about millimeter when the crest potential to be rectified is of theorder of 15,000 volts. It is to be understood that the anode chambermust be made longer, or the diameter of the orifice smaller, as thevoltage to be rectified is increased. Under best operating conditions anarc discharge will not pass from the anode to the cathode until switch32 is closed to connect togethercontrol and anode electrodes, andintermittent discharges can be stopped by opening this switch. Theinitial potential, or the potential necessary upon the control electrodefor causing a discharge between the anode and the cathode, may bedecreased by increasing the current thru the electrical heater 42I.

Fig. shows a modification of the construction shown in Figs. 1 and 3,particularly with respect to the construction of the control electrode,and to the arrangement of maintaining a condition of ionization in thecathode chamber. As in the construction of Fig. 3 the electrode providedby the cooling jacket 5!!! does not extend close enough to'the anode fordielectric current passing thru it to break down the initial resistanceof the anode chamber caused by fading due to the low gas pressureproduced by the cooling medium. The break down of this resistance isaccomplished however by utilizing an external metal sheath or coating'12 which surrounds that part of the tube adjacent to the anode 5l4l,and which also surrounds at least a portion of the jacket 5l9. By meansof conductor 13, this coating 12 is connected together with terminal 28from jacket 5l9. The. tube 521 leading from the cathode chamber isprovided with a restriction or orifice 538, similar to the orifice shownin. Figs. 2 and 3. Positioned over the end of this orifice there is aninverted cap-shaped deflector 528' which is preferably made ofinsulating material such as glass, and is supported from the dependingglass tube 16. Extending downwardly into tube 521 thru the orifice 538,there is a conductor 11, which for convenience, may be sealed into thedeflecting cap 528 and connected to the terminal conductor 49.

In the operation of that modification of the invention shown in Fig. 5,a keep alive current may be applied across the cathode and conductor 49,so as to maintain the vapor in the cathode in ionized condition. Theheat developed by this ionized current passing thru the mercury vapor,superheats the vapor which passes up thru the orifice 538. By means ofthis device I have been able tosubstantiallyreduce the reignitionpotential of the device.

Fig.6 shows a modified form of the ionizing anode shown in Fig. 4. Theanode I! in Fig. 5

' may cause overheating of the walls of the oathode chamber. To preventdeleterious results due to such overheating, I provide the upper end ofthe tube 621 with a tip or shield 18 which is made of some materialcapable of withstanding a high temperature, as for example graphite ortungsten. This tip 18 is provided with an orifice 638 thru which extendsthe ionizing anode 611, this anode being preferably constructed of metalcapable of withstanding high temperature, such as tungsten. In thisimproved construction the nature of the tip 18 and the ionizing anodepermits the vapor passing up thru the orifice 638 to be highlysuperheated.

Fig. 7 shows another modified form of the ionizing anode shown in Fig.6. In this case the vapor deflecting cap I28 is elongated and-the tipI18 terminates short of the electrode 111. The tip H8 is preferablyconstructed of quartz, which is fused to the tube 121 by a graded quartzto pyrex joint 8|. The high fusing temperature of quartz permits a highcurrent density in the orifice 138, and the high temperature of thisorifice superheats the vapor passing thru it.

In Fig. 8, I have shown a modification of the construction shown in Fig.l in that the anode may be directly cooled by circulating liquid. Thisanode. M4 is constructed of hollow metal thru which water may becirculated thru the intake and discharge pipes 83 and 84. The lower endof the electrode is of course sealed, and a metal to glass sealed joint85 is provided between a flange on the anode and the adjacent walls ofthe tube.

The use of a water cooled anode is desirable in that it reduces thepressure within the anode chamber 8l2 and thereby increases potentialrequired to produce an inverse discharge. The defleeting cap 828 in thisinstance is of slightly modified construction in that it is supported bya tungsten wire 86 extending down thru orifice 838 and secured to thewall of tube 821.

' Fig. 9 shows a modfiication of the construction shown in Figure 1 inwhich the cathode chamber M3 is extended and is surrounded by part ofthe anode chamber 9l2, as is shown. In this case to form a completecontrol electrode, a shield 912 surrounds the Walls of the anode chamberSH and also surrounds at least a portion of the cooling jacket Bill. Theelectrical heater 944 is disposed within a horizontal pocket 943 and isthus surrounded by the mercury 9H. Mercury vapor from the cathodechamber is discharged thru tube 921 at a point in the space surroundedby the cooling jacket GIS, and the tube at this point is tipped so thatthe condensed mercury may drain back into the cathode chamber thru adrain tube 929 As in the case of Figure l, the walls of the cathodechamber are preferably provided with a heat insulating jacket 946.

I claim:

l. The method of operating a mercury vapor tube having anode and cathodechambers comprising: establishing a high resistance in the anode chamberby cooling the chamber to the extent that said resistance'cannot bebroken down by a potential of ten thousand volts in the presence of aheated cathode chamber, and breaking down said resistance by piloting adischarge thru said chambers.

2. A vacuum tube having: anode and cathode electrodes for the passage ofcurrent periodically and intermittently therebetween, a discharge pathbetween said electrodes thru an ionizable vapor, a surface capable ofassuming a varying electrical charge positioned adjacent said path,means for connecting said surface to the anode comprising impedance ofhigh enough value to prevent the flow of objectionable parasiticvariable current therethru when sixty cycle alternating voltage isimpressed on said electrodes, and means for artificially reducing thevapor pressure in the vicinity of said surface.

3. A mercury arc vacuum tube arranged to pass current periodica y,intermittently, and unidirectionally compr c a solid anode in an anodechamber, a liquid-cooled wall arranged to reduce the vapor pressure insaid chamber, and a cathode of mercury arranged to be periodicallyreignitedwith the aid of a heat conductor adjacent said mercury, and asource of heat of surficiently high temperature to heat said mercurythru said conductor to the extent that the potential required to beimpressed between said electrodes to produce said reignitions isreduced.

4. A mercury vapor arc rectifier tube comprising an anode in an anodechamber, a mercury cathode in a cathode chamber, means for liquidcooling to reduce the vapor pressure in said anode chamber, means forheating said cathode by causing emission of electrons therefromintermittently and periodically, and means for heat insulating saidcathode chamber to the extent required to keep said cathode hot enoughto allow breakdown between said electrodes at the operating voltage ofthe rectifier.

5. An arc vacuum tube arranged to pass current unidirectionally andintermittently to a cathode during operation thereof comprising an anodechamber, a cathode chamber containing mercury, means for vaporizing themercury, and means including a suitable vapor-flow path for restrictingthe flow of mercury vapor from said cathode chamber to the extent thatthe vapor pressure in said cathode chamber is high enough to be brokendown by the operating voltage.

6. The method of operating a vacuum tube containing an anode, a cathodeof mercury, and

a discharge path therebetween, which comprises: heating said mercury tothe extent that self-ignition takes place at the operating voltage ofthe tube and simultaneously cooling part of said path to the extent thatsaid voltage cannot produce inverse current of excessively large'value.

7. The method of operating a vacuum tube provided with a cathode, ananode, a discharge path containing vapor, and a plurality of pilotingelements arrangedlongitudinally along said path, which comprises:establishing a relatively high pressure-gradient in said path, producinga discharge from the piloting element nearest the cathode to initiate adischarge from the next adjacent piloting element, and so on toward theanode until a main discharge from the anode to the cathode is initiated,and repeating said initiation of the main discharge periodically.

8. A vacuum tube comprising: an anode, a cathode, a discharge paththerebetween containing vapor, a cooling medium adjacent to at least apart of said path, a discharge-path control electrode comprising aplurality of elemental control surfaces disposed along said part atpoints having a substantially different electrical breakdown value withrespect to the cathode and at least one of said values being influencedby cooling, and impedances in series with each of said surfaces arrangedso that when a positive potential with respect to the cathode isimpressed on said electrode the discharge starts from one of saidsurfaces and progresses to another of said surfaces having a higherbreakdown value.

9. A mercury vapor tube comprising an electrode of mercury, means forvaporizing said mercury, a mercury-vapor condensing surface, andmeansincluding a receiving gas chamber maintained at less than atmosphericpressure for producing Sprengel pump action with mercury from saidcondensing surface.

10. The method of operating a vacuum container containing a pool ofmercury which comprises heating the mercury to vaporize it, reducing thetemperature of the vapor to condense it, and compressing fixed 'gas andstoring it at a pressure below atmospheric to produce Sprengel pumpaction while returning said condensed mercury to said pool.

11. A vacuum tube comprising an electricaldischarge path, a flow ofrelatively high pressure vapor in part of said path, a main condensingsurface, and a vapor deflector arranged todeflect said flow toward saidsurface and to divide said path into highpressure and low pressureparts.

12. The method of decreasing the inverse current caused by the highvalue of the frequency of alternating potential impressed-upon adischarge path between an anode disposed adjacent to low pressure vapor,and a cathode, which comprises: heating the cathode, establishing aninitial dielectric strength of said path sufiiciently high to preventbreakdown by the operating potential in the presence of the heatedcathode, and impressing a potential of a positive average-value such asthe operating-potential on the anode with respect to the cathode whilealternately producing at said frequency a decrease and an increase inthe electrical breakdown value of said path to thereby decrease theinverse current flow.

13. The method of reducing the pressure of fixed gas adjacent to ananode before starting to operate a vacuum tube having a solid anode anda vaporizable cathode, which comprises the following two steps in aconvenient order: heating the cathode to produce a suitable pressure ofvapor, cooling a space between the anode and the cathode to reduce thegas pressure adjacent the anode then and thereby, producing diffusionpump action with said vapor to further reduce said gas pressure, and thefinal step ofstarting intermittent flow of current from said anode.

14. A vacuum tube arranged to pass current periodically, intermittently,and unidirectionally, comprising: an anode, a cathode, a discharge paththerebetween containing gas, and a discharge-path control conductorextending in and along said path from a point having a relatively highelectrical breakdown value to a point having a lower value with respectto the cathode and possessing sufficient impedance to render inversecurrent flow negligible, said lower value being influenced by theresidual ionization produced by a preceding discharge thru said path.

15. A vacuum tube arranged to pass current periodically, intermittently,and unidirectionally, comprising: an anode, a cathode, a discharge paththerebetween containing vapor, an electrical breakdown control surfaceadjacent to at least a part of said path, and cooling means capable ofreducing vapor pressure in said part; said surface being charged to apotential having a negative average-value with respect to the anode andthe anode being periodically charged positively with respect to thecathode.

16.'A vacuum tube constructed with fused insulation-to-metal joints toprevent air-leakage, comprising: an anode, a cathode, a discharge paththerebetween containing vapor, and a surface capable of being chargeddisposed adjacent to at least a part of said path. in combination with acooling medium arranged to cool said part; the anode and said surfacebeing simultaneously charged negatively with respect to the cathode andthe anode being charged to a negative average value with respect to thecathode.

17. The method of operating a vacuum tube 'containing mercury whichcomprises heating the mercury to produce vapor at a pressurecorresponding to a relatively low electrical breakdown value, andcyclically impressing a potential of said value on the vapor to break itdown periodically by simultaneously decreasing the negativity of thespace charge of the vapor as described and increasing the ionization atthe cathode at the beginning of each cycle.

18. A vacuum tube containing mercury vapor and comprising a condensingchamber having wall surface heated only by vapor, a cathode of 7mercury, an anode, and a discharge path therebetween provided with aconstricted part having the property of tending to interruptperiodically the flow of continuous current thru said part; a potentialof positive average value being impressed on the anode with respect tothe cathodeand of high enough crest-value to break down said part aftereach interruption of current therethru.

19. A vacuum tube for passing current intermittently, periodically, andunidirectionally between electrodes, comprising: an anode in an anodespace, a discharge path terminating at the anode and containing vapor,cooling means for reducing the pressure in saidspace by cooling at leastpart of said path, a surface adjacent to, and between the terminals of,said path and arranged for increasing the electrical breakdown valuethereof, and a surface adjacent to, and between the terminals of, saidpath and arranged for neutralizing the effect of said increase.

20. The method of operating a vacuum tube containing mercury andprovided with electrodes, which comprises: heating mercury in a vacuumto the extent that self-ignition would take place between an anode andsaid mercury at the operating voltage which voltage is of such a valuethat self ignition would not occur without heating the mercury andimpressing the operating voltage between an anode and the heated mercuryto pass current periodically, intermittently, and unidirectionallytherebetween.

21. A vacuum tube for passing current periodically, intermittently, andunidirectionally thru vapor, comprising: vapor, an anode, a cathode, adischarge path therethru and therebetween having a highpressure-gradient, a control surface adjacent to the high pressure endof said path capable of decreasing the electrical breakdown value of thepath, and a control surface adjacent to the low pressure end of saidpath capable of increasing the electrical breakdown value of the path toprevent inverse current.

22. The method of operating a mercury vapor tube containing twoelectrodes and a discharge path therebetween divided into high and lowpressure parts by a condensing chamber disposed adjacent to said path,which comprises the step of decreasing the electrical breakdown value ofthe path at a point therein differing in pressure from that surroundingeither of said electrodes to initiate a main discharge therethru.-

23. In a vacuum tube: a condensing chamber, an anode, and a dischargepath terminating at said anode; said path containing vapor, and beingdivided into high and low pressure parts by passing adjacent to saidchamber, and a composite surface comprising a plurality of elementalsurfaces disposed in said parts, each capable of decreasing theelectrical breakdown value of the path to aid initiation of a maindischarge therethru.

24. The method of reducing the voltage required to initiate electronflow thru a discharge path between two electrodes, containing vapor,

\ and divided into high and low pressure parts by a condensing chamber'disposed adjacent to said path, which comprises the step of decreasingthe electrical breakdown value of the path at a plurality of pointstherein between the electrodes.

25. A vacuum tube arranged to pass current periodically, intermittently,and unidirectionally from an anode charged to a positive averagepotential with respect to a cathode comprising said anode, said cathode,a discharge path therebetween containing vapor, a cooling mediumarranged to reduce the pressure of vapor in the anode end of said path,and a surface capable of increasing the potential required to initiatecurrent flow from the anode combined with a con ductor, having highimpedance and capable of conducting continuous current, connectedbetween said surface and a source of potential having a negative averagevalue with respect to said anode.

26. The method of outgassing mercury having all of its surfaces exposedto a pressure less than atmospheric in a vacuum container whichcomprises: maintaining a foreign gas pressure in said container of thelow value described, evaporating mercury from a pool of mercury in saidcontainer to produce mercury vapor, impressing a potentialexceeding onethousand volts on said vapor with respect to a charged surface to aid indissociating said gas and vapor, condensing said vapor, and collectingsaid condensed mercury in a pool containing only mercury so treatedwhile permanently removing foreign gas from said vapor.

27. A mercury vapor container constructed with fused insulation-to-metaljoints to maintain the low pressure described comprising: a pool ofmercury constituting a source of vapor, means including a chargedsurface for electrifying the vapor, means for condensing said vaporbefore it reaches said surface, and means for forming a second pool ofmercury consisting entirely of said condensed mercury and having all ofits surfaces exposed to less than atmospheric pressure.

28. A vacuum tube comprlsing a mercury cathode, an anode, a condensingchamber, a discharge path between the anode and the cathode, meansincluding said chamber for dividing said path into high and low pressureparts, and means for reducing the value of a transient positive voltagerequired to be impressed on the anode with respect to the cathode toinitiate unidirectional discharge in said path combined with a source oftransient voltage capable of producing breakdown of the path during eachpositive half-wave impulse.

29. In a system for electron discharge a vacuum tube comprising an anodeand a discharge path terminating at said anode and containing a single,cooled, constricted passageway inclosing a surface capable of collectingpositive ions proximate thereto, and electrical energy supply for

